The present invention relates to a system for supporting nozzle diaphragms in turbines enabling the nozzle diaphragms to be secured to one another along the horizontal midline joint and particularly relates to a support system for nozzle diaphragms enabling limited, generally vertical displacement of the diaphragms relative to the outer housing.
Screw support systems presently employed to support turbine diaphragms from the outer housing in certain turbines do not permit the upper and lower diaphragm sections to be secured or bolted to one another at the horizontal joint. Because of this, there is a potential for steam leakage across the horizontal joint of the nozzle diaphragm. In these prior screw support systems, a support screw is threaded into the opposite sides of the lower diaphragm adjacent the horizontal midline joint. The head of the support screw is internally threaded and receives a set screw. When the lower diaphragm is disposed in the lower shell of the housing, the head of the support screw and the set screw are received in a slot of the lower shell. The bottom of the set screw rests on a support surface of the lower shell, supporting the lower diaphragm within the shell.
With the upper shell of the housing inverted, the upper diaphragm is disposed within the upper shell. A lug is inserted into a slot along the edge of the upper diaphragm adjacent the midline horizontal joint. The lug is bolted to the upper shell. An adjustable set screw is threaded into a threaded opening in the upper diaphragm. Upon inversion of the upper shell and diaphragm for completing the assembly of the turbine, the upper diaphragm rests on the lower diaphragm at the horizontal midline with a clearance between the upper end of the set screw and the lower face of the lug. This clearance, for example, on the order of 0.005-0.007xe2x80x3, enables displacement of the upper and lower diaphragms relative to the housing, limited only by the clearance between the set screw and the lug. With the upper and lower diaphragms not directly secured to one another, there is a potential for steam leakage at the horizontal mid-joint between the diaphragm halves.
In accordance with a preferred embodiment of the present invention, the upper and lower diaphragm halves may be secured, for example, by bolts to one another to minimize or eliminate the potential for steam leakage therebetween, while enabling the diaphragm for vertical displacement relative to the housing. To accomplish this, the upper lugs, bolts and set screws at opposite sides of the joint midline, as previously required, are entirely eliminated. Rather, only a support screw and set screw are provided adjacent each of the opposite sides of the lower diaphragm. Particularly, at each opposite side of the lower diaphragm, a support screw threads into the lower diaphragm and has a head with an internally threaded bore for receiving an elongated set screw. The set screw is dimensioned such that the depth of the slot in the outer shell which receives the set screw exceeds the length of the set screw by the predetermined clearance, for example, 0.005-0.007xe2x80x3. That is, the set screw is sized to the depth of the slot less 0.005-0.007xe2x80x3.
When installing the diaphragms, the upper and lower diaphragms are first bolted to one another. With the set screws in the threaded bores of the support screws previously threaded into the lower diaphragm, the lower diaphragm is set in the lower shell. The lower end of the set screw supports the upper and lower diaphragms within the lower shell. The upper shell is then disposed about the upper diaphragm and bolted to the lower shell at the horizontal midline, leaving a clearance between the upper end of the set screw and the horizontal midline joint face of the upper shell. Consequently, the diaphragms are supported by the set screws and the clearance limits the vertical displacement of the diaphragm halves relative to the housing.
In a preferred embodiment according to the present invention, there is provided a support system for diaphragms of a turbine, comprising upper and lower diaphragms secured to one another along a horizontal midline, a turbine housing including upper and lower outer shells for securement to one another along a midline and in surrounding relation to the diaphragms, support cooperable between the lower diaphragm and the lower shell adjacent the midlines of the shells and diaphragms, respectively, for supporting the diaphragms within the housing, each support including a set screw adjustable to provide a predetermined clearance between the set screw and a portion of the upper shell, enabling generally vertical joint movement of the upper and lower diaphragms relative to the surrounding housing, the set screw being engageable with the upper shell portion upon upward displacement of the upper and lower diaphragms within the housing to limit displacement thereof to the clearance.
In a further preferred embodiment according to the present invention, there is provided a method of supporting upper and lower diaphragms joined one to the other adjacent a horizontal midline joint and disposed within a housing having upper and lower shells surrounding the diaphragms and joined to one another adjacent a horizontal midline, comprising the steps of supporting the upper and lower diaphragms from supports projecting outwardly along opposite sides of the lower diaphragm and engaging the lower shell and limiting upper displacement of the upper and lower diaphragms within the housing by spacing an element carried by the lower diaphragm a predetermined clearance from a stop carried by the upper shell.